Document use of weights.bin

I'm interested in experimenting with the weights.bin file. Could you document the format of the file and how to create one?
I might then be able to create a PR to allow to pass in a flag through the command line to enable weights.

Locate weights.bin in the repository and trace how it is currently consumed or created. Document the file format and the steps needed to create one, then verify the instructions by following them; the command-line flag is described as a possible later PR rather than part of this documentation request.

Written by the indexing model from the issue text.